Rapid start-up of nitrogen and organic matter removal in sequencing batch biofilm reactors treating hypersaline mustard tuber wastewater with autochthonous microorganisms

Abstract

The treatment of hypersaline industrial wastewater (≥50 g NaCl L⁻¹) faces persistent challenges in start-up and nitrogen removal efficiency due to microbial inhibition under extreme salinity. However, leveraging native microbial consortia for rapid system establishment remains underexplored. This study proposed a rapid-start strategy for sequencing batch biofilm reactors (SBBRs) treating hypersaline mustard tuber wastewater (MTWW) through in-situ enrichment of autochthonous microorganisms in MTWW. Five SBBRs, each with distinct inoculation (municipal sludge vs. autochthonous microorganisms) and salinity-increase strategies (direct vs. gradual increase), were systematically compared. Systems acclimated with autochthonous microorganisms achieved start-up within 30 days (Phase Ⅰ:0–30 g NaCl L⁻¹ and Phase Ⅱ: 30–70 g NaCl L⁻¹), with COD and TN removal efficiencies of 82.40 %–92.85 % and 85.72 %–94.68 %, respectively. Notably, rapid-start systems maintained comparable TN and COD removal to gradual acclimation (p > 0.05) despite transient nitrification instability during dissolved oxygen fluctuations (recovered within 5∼6 cycles). The rapid-start reactors demonstrated greater ammonia oxidation activity, driven by the dominance of ammonia-oxidizing archaea (AOA) over bacteria (AOB). Rapid salinity increases selectively enriched halophilic functional bacteria, such as Halomonas, Nitratireductor, Arcobacter, and Phaeodactylibacter, supporting anoxic/aerobic and sulfur-driven autotrophic denitrification processes. Most of the functional microorganisms across all reactors originated directly from the MTWW, confirming the indispensability of autochthonous inoculum. Our findings demonstrate that autochthonous microorganisms in hypersaline MTWW can be directly engineered for rapid system establishment, bypassing lengthy acclimation. This strategy reduces start-up costs and provides a scalable solution for industries requiring immediate hypersaline wastewater treatment capacity.